Immunology: T Cell Activation Quiz
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Questions and Answers

What is the primary function of adhesion molecules in T cell activation?

  • Presenting antigens to T cells
  • Strengthening the interaction between T cells and target cells (correct)
  • Secreting cytokines to regulate T cell function
  • Recognizing specific antigens on target cells

    • What happens to a naive T cell when it receives a TCR signal but lacks co-stimulation?

  • The cell undergoes clonal expansion and differentiates into effector T cells.
  • The cell remains dormant and awaits further signals.
  • The cell becomes anergic or undergoes apoptosis. (correct)
  • The cell differentiates into a memory T cell.

    • Which of the following is NOT a mechanism by which partial T cell activation without co-stimulation contributes to immune tolerance?

  • Eliminating self-reactive T cells in the thymus
  • Preventing the activation of T cells against harmless antigens.
  • Promoting the development of tolerance to self-proteins
  • Inducing T cell proliferation and differentiation (correct)

    • Which molecule expressed on the surface of T cells interacts with co-stimulatory molecules on APCs?

    <p>CD28 (A)</p> Signup and view all the answers

    What type of T cell is activated by the interaction of its TCR with antigenic peptide presented by Class II MHC molecules on APCs?

    <p>Helper T cells (A)</p> Signup and view all the answers

    What is the primary function of the CD3 complex in T cell activation?

    <p>To transduce signals from the TCR to activate the T cell (B)</p> Signup and view all the answers

    What are the polypeptide chains found in the CD3 complex?

    <p>γ, δ, ε, ξ (D)</p> Signup and view all the answers

    Which of the following proteins are co-receptors for the TCR, facilitating its interaction with MHC molecules?

    <p>CD4 and CD8 (C)</p> Signup and view all the answers

    What is the primary distinction between CD4 and CD8 proteins in terms of their function?

    <p>CD4 binds to class II MHC molecules, while CD8 binds to class I MHC molecules. (C)</p> Signup and view all the answers

    Which of the following proteins is involved in the activation of cytotoxic T cells?

    <p>CD8 (C)</p> Signup and view all the answers

    Which of the following accessory molecules is expressed on memory T cells?

    <p>CD45RO (D)</p> Signup and view all the answers

    What is the primary role of CD28 in T cell activation?

    <p>To co-stimulate T cell activation (C)</p> Signup and view all the answers

    What is the role of CD154 (CD40L) in T cell activation?

    <p>To signal to antigen-presenting cells (APCs) (A)</p> Signup and view all the answers

    What is a defining characteristic of TH17 cells?

    <p>They produce cytokines such as IL-17, IL-22, and TNF-α. (B)</p> Signup and view all the answers

    What is the primary role of Tfh cells in the immune system?

    <p>To provide co-stimulation to B cells to produce antibodies. (C)</p> Signup and view all the answers

    Which of the following statements is true about TH9 cells?

    <p>They are induced by TGF-β and IL-4 and secrete IL-9. (B)</p> Signup and view all the answers

    What is a key difference between Th17 and Treg cell responses?

    <p>Th17 cells are involved in autoimmune diseases, while Treg cells suppress autoimmune responses. (D)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of Treg cells?

    <p>They produce IL-17 and IL-22. (A)</p> Signup and view all the answers

    Which type of T cell subset plays a crucial role in the development of antibodies against foreign pathogens?

    <p>Tfh cells (A)</p> Signup and view all the answers

    Which of the following is NOT a cytokine produced by TH17 cells?

    <p>IL-21 (B)</p> Signup and view all the answers

    What is the primary function of IL-9, a cytokine produced by TH9 cells?

    <p>Facilitation of antitumor responses. (A), Mediation of immune response to parasites. (B)</p> Signup and view all the answers

    Which of the following cytokines is NOT directly produced by TH2 cells?

    <p>IL-12 (A)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of the TH1 response?

    <p>Production of IgE antibodies (A)</p> Signup and view all the answers

    In the context of antigen presentation, what is the role of CD40L on the T cell?

    <p>Binds to CD40 on antigen-presenting cells to enhance their activation (B)</p> Signup and view all the answers

    What is the main function of TH1 cells in the immune response?

    <p>Control intracellular infections and activate cytotoxic T cells (B)</p> Signup and view all the answers

    Which of the following is TRUE regarding the TH2 response?

    <p>It can exacerbate intracellular infections by suppressing TH1 responses (D)</p> Signup and view all the answers

    What is the role of IL-12 in the immune response?

    <p>Promote activation of TH1 cells and inhibit TH2 differentiation (C)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of TH2 responses?

    <p>Activation of NK cells and cytotoxic T cells to kill infected cells (C)</p> Signup and view all the answers

    The interaction between CD40L on the T cell and CD40 on the antigen-presenting cell is important for:

    <p>Enhancing the activation of antigen-presenting cells (C)</p> Signup and view all the answers

    Which of the following is TRUE regarding the balance between TH1 and TH2 responses?

    <p>TH1 cytokines stimulate their own production and downregulate TH2 differentiation, leading to a feedback loop (D)</p> Signup and view all the answers

    What is the main function of cytotoxic T lymphocytes (CTLs)?

    <p>To directly kill virally infected cells and tumor cells (D)</p> Signup and view all the answers

    What is the role of perforin in the killing of target cells by CTLs?

    <p>Perforin creates holes in the target cell membrane, allowing granzymes to enter and induce apoptosis (B)</p> Signup and view all the answers

    What is the role of antigen-presenting DCs in the activation of CD8 T cells?

    <p>DCs present antigens on MHC I to CD8 T cells, leading to their activation (C)</p> Signup and view all the answers

    Which of the following is a shared feature of both antibody-dependent and antibody-independent cytotoxicity?

    <p>Both involve the release of cytotoxic granules containing perforin and granzymes (B)</p> Signup and view all the answers

    Flashcards

    FasL

    A ligand that interacts with its receptor to induce apoptosis in target cells.

    Adhesion Molecules

    Proteins that enhance T cell interaction with APCs, promoting activation.

    CD4 Helper T Cells

    A subset of T cells activated by class II MHC-peptide interactions.

    Co-stimulatory Signal

    An essential signal for T cell activation, often involving CD28 on T cells.

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    Anergy

    A state of T cell unresponsiveness due to lack of necessary co-stimulation.

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    CD8 T cells

    Cytotoxic T lymphocytes that eliminate infected/tumor cells.

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    Cytotoxic T lymphocytes (CTLs)

    Activated CD8 T cells that kill infected or cancerous cells.

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    Perforin

    A protein that forms pores in target cell membranes to induce apoptosis.

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    NKT cells

    Hybrid cells with NK and T cell characteristics, important for initial immune response.

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    Granzyme

    Toxic enzymes released by CTLs to induce apoptosis in target cells.

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    CTLA-4 Binding

    CTLA-4 binding to B7 can cause T cell anergy.

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    Antigen Presentation

    Interaction between T cells and APC allows signaling via CD40L and CD28.

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    CD4 T Cell Activation

    Activated CD4 T cells can migrate to sites in blood or lymphoid tissues.

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    TH Cell Cytokines

    TH cell types are classified by the cytokines they secrete.

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    IL-12 Role in TH1

    IL-12 is required for the activation of TH1 response.

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    TH1 Cytokine Production

    TH1 cells produce IL-2, IFN-γ, and TNF-β.

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    Function of Fas Ligand

    Fas ligand on TH1 cells induces apoptosis in target cells.

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    TH1 Response Characteristics

    TH1 response activates cellular and antibody responses early in infection.

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    TH2 Response Timing

    TH2 response occurs later and promotes antibody-mediated responses.

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    Role of IL-4 in TH2

    IL-4 pushes TH2 response and affects B cell Ig production.

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    TH17 cells

    A subset of CD4+ T cells that produce cytokines IL-17 and IL-22, involved in antibacterial and antifungal responses.

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    Cytokines produced by TH17

    TH17 cells produce IL-17, IL-22, IL-6, TNF-α, and proinflammatory chemokines essential for immune response.

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    Autoimmune diseases related to TH17

    TH17 responses are linked to autoimmune inflammatory diseases like rheumatoid arthritis.

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    Treg cells

    CD4+ CD25+ cells that suppress immune responses and prevent autoimmunity by producing TGF-β and IL-10.

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    Function of T follicular helper cells (Tfh)

    Tfh cells help B cells produce antibodies and provide co-stimulation through CD40-CD40L interaction.

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    Presence of Tfh in autoimmune diseases

    The number of circulating Tfh cells increases in patients with autoimmune diseases like lupus and rheumatoid arthritis.

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    TH9 cells

    A new subset of CD4+ T cells, induced by TGF-β and IL-4, that produce IL-9 and are involved in immune-related diseases.

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    Role of Th9 cells

    Th9 cells facilitate antitumor responses and are implicated in various immune-related conditions.

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    TCR Complex

    Combination of TCR and CD3 responsible for T cell activation and antigen recognition.

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    TCR Structure

    Each TCR has variable and constant regions, made of two polypeptide chains, identifying specific antigens.

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    TCR Repertoire

    The vast array of TCRs can recognize approximately 10^15 different epitopes.

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    CD3 Complex

    Found on all T cells, it transmits signals from the TCR to activate T cells.

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    CD4 and CD8

    Co-receptors that help TCR recognize MHC molecules on antigen-presenting cells.

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    CD4 Binding

    CD4 binds to class II MHC molecules on antigen-presenting cells, enhancing T cell activation.

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    CD8 Binding

    CD8 binds to class I MHC molecules on target cells, crucial for cytotoxic T cell function.

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    Accessory Molecules

    Additional proteins that assist T cells in interacting and activating, including CD45, CD28, and CD154.

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    Study Notes

    Cellular Immunity

    • Cellular immunity is a type of immune response that involves the activation of specialized cells to fight off pathogens.
    • T cells play a crucial role in this process. They recognize specific antigens presented by other cells in the body, initiating a tailored response to the threat.

    Cell Surface Receptors of T cells

    • The T cell receptor (TCR) complex is crucial for antigen recognition and activation. This complex consists of the TCR itself, a structure uniquely designed to recognize specific antigens, and the CD3 complex, which facilitates activation signals.
    • Each TCR molecule is made up of two different polypeptide chains, similar to antibodies, each with a constant and a variable region. The variable region allows for a vast diversity of TCRs, each capable of recognizing a different antigen.
    • The repertoire of TCRs is exceptionally large, capable of recognizing an estimated 1015 separate epitopes (parts of antigens).
    • CD3, a complex on the T-cell surface, is part of the TCR complex. It relays the signals triggered by the TCR interacting with an antigen. It's found on all T cells. The CD3 complex consists of ?, ?, ?, and ? polypeptide chains.
    • The TCR is the primary tool for the T cell to recognize specific antigens.
    • The CD3 complex is the crucial component for transduction of signals from TCR to the interior of the T cell.

    T-cell Activation

    • Several steps are involved in T cell activation.
    • The CD3 complex activates specific transcription factors in the nucleus of the T cell, which leads to the T cell activation.
    • This activation also triggers the production of inflammatory mediators, including cytokines such as IL-12, IL-2, and their respective receptors(IL-2R).

    TH Cell Activation

    • Helper T (TH) cells require two signals for activation: interaction of the T cell receptor (TCR) with an antigen presented by a major histocompatibility complex (MHC)II molecule, and co-stimulatory signals, which involve CD28 on the T cell binding to proteins on the antigen-presenting cell (APC).
    • The binding of MHC to the T-cell receptor triggers ITAM phosphorylation.
    • ZAP-70 binds and is phosphorylated by this phosphorylation.

    CD4/CD8 T cell activation

    • CD8 binds to the α3 domain of MHC class I molecules of target cells
    • CD4 binds to the β2 domain of MHC class II, presented by antigen-presenting cells.

    Cell Surface Receptors of T cells (Accessory molecules)

    • Accessory molecules expressed on T cells include CD4, CD8, proteins that act as co-receptors for the TCR, assisting in antigen recognition for T-cells, enhancing activation, and promoting interactions between T cells and antigen presenting cells (APCs) and target cells.
    • Other accessory receptors include CD45RA (naive T cells) or CD45RO (memory T cells), CD28 or CTLA-4 (cytotoxic T-cell-associated protein 4), CD154 (CD40L), and FasL, all which play different roles in T-cell function, activation and interaction with other immune cells.

    Adhesion Molecules

    • Adhesion molecules, like LFA-1, help T cells adhere more tightly to antigen-presenting cells (APCs), ensuring effective interaction and activation.
    • Adhesion molecules aid in tight interactions between T cells and APCs.
    • These molecules include leukocyte function-associated antigen-1 (LFA-1) that interacts with intercellular adhesion molecules (ICAMs), further strengthening the interaction between T cells and APCs.

    Initiation of T Cell Responses

    • T cell responses are initiated by antigen-presenting cells (APCs), such as dendritic cells (DCs).
    • Helper T cells (CD4 T cells) are activated by the interaction between their TCR and antigenic peptides presented by MHC class II molecules on APCs.
    • Co-stimulation, mediated by CD28 on T cells interacting with B7 molecules on APCs, is required for T cell activation and proliferation and growth.

    Helper T-cell Subsets

    • Different types of helper T cells (TH1, TH2, TH17, Treg, Tfh, Th9) arise from common precursor cells, and are characterized by the cytokines they produce:
      • TH1 cells mediate responses to intracellular pathogens and activate cytotoxic T cells and macrophages
      • TH2 cells mediate responses to extracellular pathogens and promote antibody production.
      • TH17 cells are involved in the inflammatory response to certain pathogens and promote inflammation.
      • T regulatory cells (Treg) suppress immune responses to help prevent autoimmunity.
      • Tfh (follicular helper T cells) provide help to B cells to produce antibodies
      • Th9 cells play a role in antitumor responses.

    Antigen Presentation to T cells

    • Naive T cell responses are initiated by antigen-presenting cells (APCs), such as dendritic cells (DCs)
    • CD4 helper T cells are activated by the interaction between TCR and antigenic peptides presented by MHC class II molecules on APCs.
    • Co-stimulatory signals are mediated by binding to proteins on APCs to CD28 molecules on the T cell, inducing T cell growth.

    The TH1 Response

    • TH1 responses occur early in the course of infection and strengthen cellular and antibody responses.
    • TH1 responses amplify local inflammatory reactions and DTH reactions, activating macrophages, NK cells, and CD8 cytotoxic T cells.
    • TH1 responses also expand the immune response by promoting growth of B and T cells with IL-12.

    The TH2 Response

    • TH2 responses act later and work through antibody-mediated responses.
    • TH2 responses occur in the absence of IL-12/IFN-Y signals.
    • TH2 cells release cytokines including IL-4, IL-5, IL-6, and IL-10, which stimulate B-cell activity.
    • These responses are involved in allergies and antibody-mediated responses to parasites.

    The TH17 Response

    • TH17 cells produce cytokines such as IL-17, IL-22, IL-6, TNF-alpha, and pro-inflammatory chemokines.
    • TH17 responses are critical for initial antibacterial and antifungal responses.
    • TH17 cells are involved in inflammatory responses in immunoprivileged sites such as the eye.

    Treg Cells

    • Treg cells are antigen-specific suppressor cells that prevent autoimmune responses by producing TGF-beta and IL-10.
    • Treg maintain immune responses under control and promote memory cell development.

    NKT cells

    • NKT cells are a hybrid between natural killer (NK) cells and T cells.
    • They express both NK cell markers and TCRs.
    • NKT cells release large amounts of IL-4 and IFN-Y and are important in initial responses to infections, particularly mycobacteria.

    CD8 T cytotoxic cell Function

    • Activated CD8 T cells, or cytotoxic T lymphocytes (CTLs) differentiate into mature CTLs and interact with target cells.
    • Granules containing cytotoxic molecules, like granzymes and perforin, are released into the target cell, inducing apoptosis.
    • Perforin creates holes in the target cell membrane, allowing granzymes to enter and trigger apoptosis.

    Cytokines and Cytokine Interactions

    • Cytokines act as inflammatory messengers, regulating the activity of multiple cells in the immune system.
    • Cytokines such as IL-12, IFN-Y, TGF-β and factors that regulate the balance between TH1 and TH2 or other immune responses play a significant role in T-cell activation, differentiation, and the development of specific immune responses.
    • Different types of helper T cells, such as TH1, TH2, TH17, and T-regulatory (Tregs) cells, exert crucial regulatory functions by secreting specific sets of cytokines. The interactions between these cytokine profiles are important parameters to control the immune system response.

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    Description

    Test your knowledge on the crucial mechanisms of T cell activation in immunology. This quiz covers adhesion molecules, TCR signaling, co-stimulation, and the roles of different T cell types. Understand the interactions that underpin the immune response and their implications for tolerance and activation.

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